Learn to Crochet - Puff Stitches
These are similar to bobbles but are worked, using half double crochet, into the same stitch or space. However, because of the way a half double crochet stitch is constructed, it cannot be worked until one loop remains on the hook. The puff stitch is not closed until the required number of stitches have been worked.
To make a three half double crochet puff stitch:
Yarn over, insert the hook in specified stitch, yarn over again and draw a loop through (three loops on hook).
(1) Repeat first step twice more, inserting the hook into the same stitch (seven loops on the hook); yarn over and pull yarn through all seven loops on the hook.
(2) As with popcorns and bulky bobbles, an extra chain stitch is often used to secure the puff stitch firmly. The pattern will tell you if this is necessary.